Prereaction of binders for quickmix processing of propellants



April 2, 1968 R. D. SHEELINE 3,376,175

PREREACTION OF BINDERS FOR QUICKMIX PROCESSING OF PRQPELLANTS FiledApril 18, 1965 Y h s O c S V SOLUBILITY SOLUBILI TY I OR VISCOSITY TIMECURATIVE TANK PRE-POLYMER TANK INVENTOR.

E N L E E H s D L L A D N A R United States Patent PREREACTION 0FBINDERS FOR QUICKMIX PROCESSING OF PROPELLANTS Randall D. Sheeline,Woodland Hills, Califi, assignor to North American Rockwell Corporation,a corporation of Delaware Filed Apr. 18, 1963, Ser. No. 274,021

2 Claims. (Cl. 149-19) This invention relates to an improvement in aprocess for dispersing solids in polymeric binder materials. Moreparticularly, the invention relates to a process for reducing thesolubility of materials in an inert carrier utilized in a process fordispersing solids in polymeric binder materials.

InUnited States Patent No. 3,022,149, there is described a process forthe manufacturing of polymers containing substantially uniformlydispersed solid materials therein. The process broadly provides at leastone dispersion of non-solvent polymerizable materials and non-solventreactant materials in a non-reactive liquid dispersion media, and atleast one dispersion of filling substances in nonsolvent andnon-reactive liquid dispersion media, the dispersion mediums beingmutually miscible, mixing the dispersions together, permitting thedispersed materials and the dispersed substances to coalesce and form anagglutinate to substantially uniformly disperse filling substances inthe polymerizable materials. Curing agents, catalysts and otheringredients besides the filling substances can be added to producecertain compositions. The mass may then be cured at ambient or elevatedtemperatures to provide a plastic polymer with dispersed solid materialtherein.

While the method described in the aforementioned patent may be performedas a batch process, it is preferred to carry out the process in acontinuous manner which eliminates the requirement for mechanicalagitation to insure thorough mixing of the polymer and the solid beingdispersed therein. This is accomplished by bringing separate streams ofthe polymeric materials and solid dispersions together into a commonstream and effecting mixing by the turbulence set up at the point atwhich the two streams join. One method of accomplishing this is bymetering a flow of one dispersion into a stream of the other dispersionas it is conducted from the dispersion container to a receiving vesselthrough a pipe or other appropriate channel.

Another method of mixing is by bringing two channels of separatedispersions together and allow mixing to be aflFected by the turbulenceset up at the point of junction of the two channels. The proportions inwhich the two dispersions are combined is controlled by regulating therate of feeding the separate components into their respective dispersingcontainers from where they flow into the channels.

The vehicles which are used as the dispersion mediums must benon-solvent with respect to the dispersed substances. The same mediummay be used for both the polymeric material and the solid substances orconversely different vehicles or dispersion mediums may be employed forthe polymer and the solid components. It is required only that thedispersion mediums for the two types of components be non-reactive toeitherthe polymeric substances or the solid material and that themediums employed for each of the polymeric and solid components bemutually miscible. It has-been found, however, that a problem ariseswith regard to the solubility of some normally-utilized binder materialsin the available dispersion mediums for the process. Any of the bindermaterial that solubilizes in a dispersion medium will not react to formthe desired product, thus it is desirable that as high a percentage ofinsolubility be reached as possible. Of course it is desired that thebinder material approach 100 percent insolubility in the carrier.

Thus, it is an object of this invention to provide a method fordecreasing the solubility of a binder and curative material in a liquidcarrier.

A further object of this invention is to provide a novel apparatus foraccomplishing a reduction in solubility of a binder and curvativematerial in a liquid carrier.

Normally, in the process involved, curing agents or catalysts are addedin minor amounts to the dispersions. Some curing catalysts normallypossess a high solubility in the carriers utilized and it is desirableto reduce this solubility. It has been discovered, and as a resultthereof forms the basis of this invention, that the solubility in thecarrier material of the prepolymer and curing agent can be greatly andunexpectedly reduced by their partial reaction prior to introductioninto the process without increasing the viscosity beyond the point thatthe product is no longer castable.

It is believed that the invention will be further understood from thefollowing description together with the drawings in which:

FIG. 1 represents a plot of viscosity or solubility versus time for thereaction of a hypothetical prepolymer and curing agent,

FIG. 2 represents the schematic outline of the system for theprereaction of the binder and curative agent utilized,

FIG. 3 is a cross-sectional view of the mixing portion of theprereactive device utilized,

FIG. 4 taken along lines 44 of FIG. 3 shows a mixing plate utilized inthe pre-reactor device.

Among the polymeric binder materials that are used in the process andwhich form the basis for the pre-reaction of this invention, substancessuch as polymerized di-(thioethoxy) methylene, silicone polymers andrubbers of the type described in a text, Chemistry of the Silicones byE. G. Rochow, 2nd ed. (1951), published by John Wiley and Sons,Incorporated, New York. An example of a silicone polymer is a siliconegum obtained by heating a hydrolysate of a mixture of mol percentdirnethyldichlorosilane and 10 mol percent of diphenyldichlorosilane inthe presence of a small amount of iron chloride. The composition issubjected to heating only for a period of time suflicient to obtain aviscous liquid. Another polymer material that can be used is an epoxycompound such as a product as obtained by the reaction of a mole of 2,2-bis(4-hydroxyphenyl)-propane with one or more mols of epichlorohydrinein the presence of a base such as sodium hydroxide. This gives aglycidyl' polyether having terminal epoxy groups. Another example of apolymeric material is a polyurethane material such as a co-polymer ofpolypropyleneglycol and toluene diisocyanate. Other examples of thepolymeric materials utilized are the telechelic polymers such ascarboxy-terminated linear polybutadiene. Further materials includehydrocarbon saturated and unsaturated resins such as the co-polymer ofbutadiene and acrylic acid, materials such as nitrocellulose andnitramine. Additionally, high nitrogen binders can be utilized such aspolyvinyl tetrazole, polyethylene hydrazine, triaminoguanidine azidereacted with aldehyde, diamino tetrazene reacted with formaldehyde. Alsofluoropolymers of the a,a,w-trihydrofluoroalkyl acrylate esters andnitroso rubbers. Other resins and polymeric substances can be used andwill be apparent to those skilled in the art.

Non-limiting examples of catalysts used for curing purposes are aluminumchloride, bis-tri-methylsilyl borate and benzoylperoxide. Other wellknown curvatives such as MAPO which is trisI-(Z-methyl)-aziridinyl]phosphine oxide and PAPI which is polymethylene,polyphenylisocyanate are additional examples of the curative materialsthat are contemplated. The curatives are added in amounts of 0.1 toabout 10 weight percent based on the weight of the polymer resin orelastomer. Preferably, 0.1 to 6 weight percent of the curative isutilized.

The vehicles which are used as dispersion mediums are those which aregenerally non-solvent with respect to the dispersed substances aspreviously described. Examples of these dispersion mediums or carrierswhich are employed include aliphatic and olefinic hydrocarbons havingabout 3 to about 16 carbon atoms. Examples of these are propane, butane,hexane, heptane, particularly n-heptane, octane, dodecane and hexadecaneas well as 2-octene, 1- dodecene, l-hexadecene, etc. Examples of cyclichydrocarbons are cyclohexane, rnethylcyclohexane, etc. Examples ofaromatic and alkyl aromatic compounds which are employed as dispersionmediums include compounds having from 1 to about 16 carbon atoms such asbenzene, toluene, zylene, 2,4-dipentabenzene, phenyldecane, decalin,l-hexyldecalin, etc. Halogen derivatives of the above hydrocarbons arealso employed as dispersion mediums. Examples of these includeethylenedichloride, trichloroethylene, methylenedichloride,chlorobenzene, bromobenzene, iodobenzene. Compounds of the Freon typesuch as dichlorodifiuoromethane and dichlorotetrafluoroethane, etc. mayalso be employed.

Other possible dispersion mediums are alcohols having from 1 to about 12carbon atoms and from 1 to about 3 hydroxyl groups. Examples of theseare methyl alcohol, ethyl alcohol, benzyl alcohol, glycerin, dodecylalcohol, etc. The means may also be used which have from about 2 toabout 12 carbon atoms and from 1 to about 3 nitrogen atoms. Theseinclude such compounds as ethylene diamine, diethylene, triamine,dodecylamine, pyridine, etc. Ethers, ketones, aldehydes and estershaving from about 2 to about 16 carbon atoms are also used. Examples ofthese are ethyl ether, acetone, propiona'ldehyde, ethyl acetate,butyldodecanoate, butylcellosolve, etc. Obviously other materials may beused as the carrier providing that they are non-reactive with the binderor curative material and that the binder and curative material arerelatively insoluble therein.

The concept of this invention is illustratively seen in the chartplotted in FIG. 1. It has been found that as the reaction time at aparticular temperature between a hypothetical prepolymer and curingagent increases, the solubility will decrease while the viscosity willincrease. If the prereaction is allowed to progress for a time rangingbetween time A and time B, a marked decrease in solubility is obtainedwithout too great an increase in viscosity. It is to be pointed out thatthe simple graph FIG. 1 is merely illustrative and is not sealed forvalues of solubility and viscosity. It is the purpose of this inventionto pro-react the curative and binder material to a time of reactionbetween the theoretical points A and B such that the solubility in thecarrier greatly decreases while the viscosity of the product of thereaction has not reached such a point where it can not be carried in theoverall continuous process involved.

The overall system for affecting the desired result of this invention isshown in FIG. 2 wherein a heated prepolymer tank and a curative tank aredisposed in relation to gear pumps or feeders 13 which feed the polymerand curative respectively into the pre-reactive section 14. The reactiveportion of the pre-reactor 14 is jacketed with a cylindrical casing 15which has an inlet 16 and outlet 17 through which hot water or steam ispassed when needed to cause a sufficient pre-reaction of the twomaterials utilized. From the pre-reactor the pre-reacted polymers andcurative pass into the mixer section 18 where it is combined withfilling substances in dispersion mediums being emitted from lines 19 and20. The resultant slurry then leaves the mixer from line 21. Alternativeto that shown the pre-reacted material may be first formed in a separatedispersion prior to entering the mixer.

Reference is now made to FIG. 3, particularly disclosing the pre-reactorportion of the device utilized to effect the desired results of thisinvention. The feed line 11 from the curative storage tank enters thehousing 22 for the pre-reactor and extends concentrically therein. Thefeed line 12 from the prepolymer storage tank terminates at the housing22 for the pre-reactor at a point intermediate of the disposed length ofthe curative feed line 11 within the pre-reactor housing 22. Thecurative material is emitted from the feed line 11 through a pluralityof radial apertures 23 situated adjacent its closed end within thepre-reactor housing 22. Upon leaving the apertures 23, the curativebegins its mixing with a prepolymer material that substantially fillsthe pre-reactor housing 22. A plurality of plates 24 are placeddownstream from the terminal end of the polymer feed line 11 within theeasing 22, three being shown by way of example. These plates, as shownin FIG. 4, are provided with a plurality of apertures 25 therein, suchapertures shown by way of example in FIG. 4 particularly. The functionof a plate within the housing is to accomplish good mixing of thecurative with the polymer material as it passes through the heatedpre-reactor. This mixing being affected by the passage of the polymerand curative through the succeeding apertures in each plate. For readyaccess, the plates 24 are secured within the housing 22 with standardfittings such as those available for use with AN tubing wherein tube 22is in section held together by AN fittings and containing plates 24 (notshown).

Example To clearly illustrate this invention, a carboxy terminatedlinear polybutadiene, which is a commonly used prepolymer, was mixed ina conventional carrier using the described process. The carrier wasisopropyl alcohol. To illustrate the solubility of the prepolymer, 20grams thereof was stirred in a beaker in grams of isopropyl alcohol forfive minutes. The beaker was maintained in a F. bath. After completionof the stirring, the alcohol was decanted from the beaker and analyzedfor nonvolatiles which would, of course, be the prepolymer. It was foundthat 0.4 gram of the prepolymer had solubilized in the alcohol carriermaterial. However, the curative MAP0 and isopropyl alcohol areessentially completely soluble in each other. A common bindercomposition consists of these two materials in the ratio of 19.4 partsof prepolymer and 0.6 part of curative. When 19.4 grams of prepolymerand 0.6 gram of MAP0 curative were mixed with isopropyl alcohol at 140F., all the MAP0 and 0.4 gram of the prepolymer dissolved in the alcoholcarrier. This clearly would indicate that the MAPO, which is ahighlydesirable curative, could not be feasibly used in the overallprocess since it would not react with the binder material if it were allin a state of solubility in the alcohol carrier. To prove thefeasibility of the invention, the prepolymer and the curative MAPO werethen metered in a 19.4:0.6 ratio into the pre-reactor device previouslydescribed. The jacket temperature was maintained at 240 F. with aresidual time of four minutes in the reacting device and then mixed withisopropyl alcohol for five minutes at 140 F. The alcohol was thendecanted from the resultant product and analyzed for non-volatilematter. It was found that only 0.2 gram of such non-volatile materialexisted in the isopropyl alcohol. Further analysis showed that nomeasureable amount of MAP0 could be found dissolved in the isopropylalcohol. The results as set forth in Table I are clearly indicative ofthe surprisingly unexpected improvement obtained from the pre-reactionof the two components.

2 Four minutes at 240 F.

It should be understood that the length of the pre-reactor, the rate offeed of the reactants, the temperature of the pre-reactor and quantitiesof materials used are all variables being this is essentially apolymeric reaction which transpires. The viscosities of the pre-reactedmaterial are often in the range of 250,000 to 500,000 centipoiscs,though by no means limited to this range. In fact, the material may beso viscous that it can be removed only by shaking. The objective hereinis to partially react the curative and the prepolymer material. Normallythe curatives and prepolymers utilized have a multiplicity of reactivegroups. For example, with the MAPO molecule there are normally anaverage of three to four reactive sites present. The objective of theherein invention is to pre-react the curative with the prepolymer so asto tie up only one, or two at the most, of the reactive sites present onthe curative with the prepolymer material. Then, after the pre-reactedcomposition polymer meets the solids fed into the mixer, and they becomea homogeneous mass, the remaining reactive sites are reacted during acuring operation, which may consist simply of heating. By the termheating, it is contemplated that the reaction may occur between ambientconditions for polymers curing at same and 300 F., though temperatureswithout this range are possible depending on the polymers.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by Way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. In a process for the manufacture of a composition comprisingsubstantially uniformly dispersed solid particulate substances in anorganic polymer, which comprises mixing, under turbulent conditions, (1)at least one dispersion of a liquid organic material in a non-reactivedispersion medium which material forms a binder upon curing with (2) atleast one dispersion of a solid particulate selected from the classconsisting of fuels and inorganic oxidizers filling substance having aparticle size of at least one micron in a non-reactive dispersionmedium, said turbulent conditions operating to combine said fillingsubstance and said liquid organic material into a dispersion on contactsuch that said dispersion, upon the release of turbulent conditions andin the absence of added colloid coagulating agents separates from saidcarrier, and upon curing said dispersion is further characterized inthat it forms a solid cohesive substance of substantially uniformcomposition, the improvement comprising intimately mixing apolymer-forming material with a curative for a sufficient period of timeto partially cure said polymer-forming material prior to forming saiddispersion (1).

2. In a process for the manufacture of mixtures of polymeric materialsand filling substances which comprises providing (1) at least onedispersion of polymerforming materials in non-reactive liquid organicdispersion mediums, wherein said polymer-forming materials consistessentially of at least one component selected from the class consistingof silicone polymers, silicone rubbers, glycidyl polyethers havingterminal epoxy groups, polyurethane material, polymerizeddi-(thioethoxy) methylene, partially polymerized materials having thegeneral formula:

in which R is a hydrocarbon group and n is a number selected from theseries, 1, 2, 3 and isocyanate resins having the general formula:

wherein n is as defined above and such that the molecular weight of theresin is from about 2,000 to about 3,000, and wherein the ratio byweight of polymer-forming materials-to-dispersion mediums in (1) is fromabout 1:19 to about 1:1 and (2) at least one dispersion of solidparticulate filling substances consisting essentially of inorganicperchlorates in non-solvent and non-reactive liquid organic dispersionmediums, said dispersion mediums being mutually miscible, providing anindividual stream of each of said dispersions, bringing said streamstogether under conditions of turbulence to form a common stream ofuniform composition, permitting said dispersed polymerized materials andsaid dispersed filling substances to coalesce and form an agglutinatedcomposition of substantially uniformly dispersed filling substances insaid polymerizable materials, the improvement comprising intimatelymixing said polymer-forming material with a curative for a sufficientperiod of time to partially cure said polymer-forming material prior toforming said dispersion.

References Cited UNITED STATES PATENTS 2,213,577 9/ 1940 Cordier260-30.2 2,282,948 5/1942 Dietzel 26030.2 2,788,337 4/1957 Preiswerk eta1 26037 2,849,417 8/1958 Tsang 26037 2,987,381 6/1961 Carter et al.23--284 3,042,500 7/ 1962 Godel 23-284 2,962,368 11/1960 Guth l49193,022,149 2/1962 Cramer 14919 3,018,203 1/1962 Guth 14919 3,296,043 l/1967 Fluke et al 14919 BENJAMIN R. PADGETT, Primary Examiner.

MORRIS LIEBAM, Examiner.

J. W. BEHRINGER, Assistant Examiner,

2. IN A PROCESS FOR THE MANUFACTURE OF MIXTURES OF POLYMERIC MATERIALSAND FILLING SUBSTANCES WHICH COMPRISES PROVIDING (1) AT LEAST ONEDISPERSION OF POLYMERFORMING MATERIALS IN NON-REACTIVE LIQUID ORGANICDISPERSION MEDIUMS, WHEREIN SAID POLYMER-FORMING MATERIALS CONSISTESSENTIALLY OF AT LEAST ONE COMPONENT SELECTED FROM THE CLASS CONSISTINGJOF SILICONE POLYMERS, SILICONE RUBBERS, GLYCIDYL POLYETHERS HAVINGTERMINAL EPOXY GROUPS, POLYURETHANE MATERIAL, POLYMERIZEDD--(THIOETHOXY) METHYLENE, PARTIALLY POLYMERIZED MATERIALS HAVING THEGENERAL FORMULA: